Multiple cathode sputtering fixture



March 24, 1970 R. s. HUMPHRIES MULTIPLE CATHODE SPUT'IERING FIXTUREFiled April 19, 196? 2 Sheets-Sheet 2 INVENTOR.

RICHARD s. HUMPHRIES ATTORNEY United States Patent 3,502,562 MULTIPLECATHODE SPUTTERING FIXTURE Richard S. Humphries, Addison, N.Y., assiguorto Corning Glass Works, Corning, N.Y., a corporation of New York FiledApr. 19, 1967, Ser. No. 631,982 Int. Cl. C23c 15/00 US. Cl. 204-298Claims ABSTRACT OF THE DISCLOSURE A multiple cathode sputtering fixtureis described which permits the simultaneous sputtering of a plurality ofcathodes. Because of the simple cathode shapes accommodated by thisfixture, even hard brittle materials are easily supported forsputtering. When diflering cathode materials are used, thin filmmixtures or alloys may be deposited.

Sputtering refers to the removal of material from a surface due toparticle bombardment and is an occurrence commonly observed at thecathode in a D.C. gas discharge. A gas, which is admitted into anevacuated chamber containing anode and cathode electrodes, ionizes uponapplication of a voltage to the electrodes. The positive ions areattracted to and bombard the negatively charged cathode resulting in aliberation of the cathode material. This phenomenon is termed cathodesputtering. The disintegrated material leaves the cathode surface eitheras free atoms or in chemical combination with the residual gasmolecules. Some of the liberated atoms are deposited on surfacessurrounding the cathode. This effect has been utilized to producehomogeneous thin films of elements, alloys or compounds on substratessuitably positioned within the evacuated chamber.

In a cathode sputtering apparatus the cathode may be suspended from thetop of the evacuated chamber and must be connected to a source of highnegative potential. Cathode materials which are mechanically strong andeasily machinable can be formed into the desired shape and supported inthe deposition chamber with little difficulty. For example, a piece ofcathode material may be formed into a disc or a cylinder and bored andtapped on the top side thereof so that a high voltage conductive rod maybe screwed therein to support the material while supplying a highvoltage thereto.

However, some materials such as silicon are not compatible with theusual drill and tap or welding operations which are required to supportthe cathode material in the deposition chamber. Furthermore,conventional cathode support devices may lack means to provide adequateelectrical contact to a semiconducting cathode material. In addition,most cathode holders can support only one piece of cathode material.

It is, therefore, an object of this invention to provide a support for abrittle cathode sputtering material.

Another object of this invention is to provide a cathode holder for acathode sputtering apparatus which permits the simultaneous sputteringof a plurality of cathodes of identical or different materials.

A further object of this invention is to provide a multiple cathodesputtering fixture which permits the use of materials such as siliconand germanium which are not compatible with the usual drill and tap orwelding operations necessary for cathode support.

Another object of this invention is to provide a support for a cathodefor use in a sputtering apparatus, the cathode material being such thatit is not easily formed into the usual cathode shapes.

Briefly, the cathode support according to this invention comprises aflat conductive holder having at least one hole therethrough, each holehaving an inwardly projecting flange at the bottom portion thereof. Theflange defines an aperture through which cathode sputtering occurs. Aconductive means is connected to the cathode holder for supporting itand for connection of a voltage thereto. Conductive shield meanssurrounding the cathode holder prevent sputtering from any point thereonexcept through the aperture at the bottom of each of the holes. A meansis provided for insulating the shield from the cathode holder.

Other objects and advantages of the invention will become apparent fromthe following detailed description, taken in connection with theaccompanying drawings, in which:

FIG. 1 is a simplified schematic elevational view, partly in section, ofan apparatus for use in thin film deposition by reactive sputtering, and

FIG. 2 is an exploded view, partly in section, of the multiple cathodesputtering fixture of this invention.

The basic apparatus required for the deposition of thin films byreactive sputtering is shown in FIG. 1. The apparatus includes asuitable vacuum chamber including a conductive cylinder 10 which isdisposed upon a conductive base plate 11 having a vacuum conduit 12connected thereto. A shaft 13 which protrudes through the base member 11rotatably supports a rotatable substrate pedestal 14 on which thesubstrates 15 and 16 are situated to be coated. A rotatable shaft 18supports a shutter 19 which may extend over a major portion of thesubstrate pedestal 14. Suitable sealing means (not shown) surround theshafts 13 and 18 to insure a retention of a vacuum within the chamber.The cylinder 10 may be sealed to the base member 11 by an annular rubbergasket 21.

Provision is made for evacuating the vacuum chamber via the vacuumconduit 12 which is controlled by a suitable valve (not shown).Furthermore, there are represented gas feeding pipes 23 and 24 whichsupply gas to a feeder pipe 29 which exhausts in the vacuum chamber. Theflow of gas in these pipes is regulated by the valves 25 and 27 Whilethe valves 26 and 28 may be used as on-olf valvesln addition to an inertgas such as argon, which ionizes and bombards the cathode, a reactivegas such as oxygen may be introduced into the chamber if it is desirableto deposit an oxide of the cathode material on the substrate.

The cathode support, which is suspended from the top of the cylinder 10in FIG. 1, is also shown in an exploded view in FIG. 2. The cathodesupport comprises three major parts, the cathode holder 31, the uppershield 32, and the lower shield 33. These three parts may be made of aconductive material such as aluminum, which does not readily sputter.The cathode holder is suspended from the top of the cylinder 10 by asteel rod 34 which is insulated from the cylinder by a rubber bushing35. The terminal portion 37 of a high voltage line 36 is secured to thesteel rod 34 by two nuts 38 and 39 which also suspend the rod 34 fromthe top of the cylinder 10. An aluminum tube 41, which is insulated fromthe steel rod by a quartz tube 42, makes an electrical connection=between the upper shield 32 and the top of the cylinder 10. Since theentire cylinder is maintained at ground potential, the shields aregrounded by the aluminum tube. The cathode holder 31 is maintained at ahigh negative potential, since it is connected to the steel rod 34.Insulation between the holder and the shields is accomplished bymaintaining the separation at all points therebetween to less than thecathode dark space for the conditions under which sputtering takes place(approximately 3 mm.). A plurality of quartz spacers 44 which aresituated in holes 45 and 46 in the cathode holder 31 and the top shield32, respectively, maintain the proper spacing between these twoelements. A plurality of setscrews 48, which are screwed into holes 49in the flanged portion of the bottom shield 33, engage a longitudinalslot 50 in the flanged portion of the top shield 32. The vertical :3displacement of the bottom shield with respect to the top shield can beadjusted by varying the vertical position of the setscrew 48 in the slot50 so that the proper spacing exists between the cathode holder 31 andthe bottom shield 33.

A plurality of holes 53 located in the cathode holder 31 have inwardlyprojecting flanged portions 54 at the bottom thereof to retain discs ofcathode material 55 which are supported therein. The annular flange 54defines a hole 56 through which the cathode material is sputtered. Aplurality of cylindrical conductive weights 58 may be inserted into theholes 53 after the cathode material 55 has been inserted therein toinsure that a good ohmic contact is made to the sputtering material.Furthermore, the height of the cylinders 58 is chosen so that the topsthereof are within the cathode dark space distance from the upper shield32 after they are inserted over the cathode material 55, so thatsputtering does not take place in the upper regions of the holes 53. Aplurality of holes 59 in the bottom shield 33 are aligned with the holes56 to permit sputtering of the cathode material 55 therethrough. Thesetscrews 48 and the quartz spacers 44 assure orientation of the lowershield to the cathode holder so that the holes in the lower side ofthese two parts are properly aligned to limit sputtering to the cathodetarget area. When less than the total number of cathodes ar used, aplate 60 may be fastened to the bottom shield by a plurality of screws52. An aperture 61 in the plate 60 exposes less than the total number ofholes in the bottom shield 33. in the disclosed embodiment, the threemost centrally located holes in the shield 33 are exposed by theaperture 61.

A speciflc example of the use of the apparatus of FIG. 1 to deposit athin film of silicon dioxide is as follows. The vacuum system within thcylinder 10 is maintained at a pressure of approximately 25 microns ofmercury. Ambient pressure is controlled by throttling the vacuum portrather than adjusting the valves 25 and 27. Thus, the gas input remainsquite constant. The cathode discs are held at about .3500 volts.resulting in a dis charge condition. The gas composition is controlledto be approximately equal parts of oxygen and an inert gas such asargon. As the voltage is applied, the inert gas ionizes upon collisionwith the electrons accelerated by the field, and the heavy positive ionsbombard the negatively charged cathodes, thereby resulting in theiiberation of target material. The removed material is oxidized by theoxygen and deposits on the substrates.

Each deposition begins with a closed shutter over the carefully cleanedsubstrates 15 and 16. A high vacuum, i.e., 10 mm. of mercury isinitially obtained followed by a pure argon backi'ill to a pressure ofapproximately 25 microns of mercury. Sputtering for a brief period inargon or other inert gas serves to prepare the initial cathode surfacefor each run. Next. a several minute sputtering cycle is run with oxygenadded to the argon flow to provide initial stability to the depositionconditions and a reproducible history for the cathode prior topredeposition. The shutter 19 is then opened and oxidized cathodematerial is deposited on the silicon substrates 15 and 16.

A cathode holder constructed in accordance with this invention permitsthe simultaneous sputtering of up to 12 cathodes of identical ordiffering materials. In one specific embodiment the holes 53 are 1% inchin diameter and the flanged portion 54 forms a 3/ inch diameter hole.The distance from the top of the hole 53 to the flange 54 is /2 inch. Inorder to sputter a material in this fixture, the material samples mustbe less than /2 inch thick, preferably but not necessarily having flatparallel top and bottom sides. The sample must also be able to drop intothe 1% inch diameter hole 53 but completely cover the con entric it-iinch diameter hole 56.

4 Almost any solid can be easily shaped to meet these requirements. Ifthe material is substantially less than V2 inch thick, the weight-spacer58 is placed over the sample to facilitate electrical contact betweenthe cathode material and the holder and to maintain close spacingbetween the cathode and the top shield.

The above described fixture has been used successfully for thedeposition of thin films of silicon and silicon dioxide. The rotatingsubstrate pedestal 14 assures uniformity of film thickness. Withplanetary substrate movement and cathodes of dissimilar materials,mixtures of uniform composition could be deposited.

What is claimed is:

l. in a cathode sputting apparatus, including a chamber, a support forholding at least one piece of cathode material within said chamber, saidsupport comprising a conductive cathode holder having at least one holetherethrough, an inwardly projecting flange extending from said holderat one end of each hole, each said flange retaining one piece of cathodematerial within its associated hole, said flange defining an aperturethrough which cathode sputtering occurs; means to support a sputteringdischarge within said chamber; conductive means connected to saidcathode holder for applying a negative potential thereto; conductiveshield means surrounding said cathode holder; means for insulating saidshield means from said cathode holder: and means for making said shieldmeans positive relative to said cathode holder for inhibiting sputteringfrom any point on said holder except through said apertures.

.2. An apparatus as described in claim 1 wherein said holder has aplurality of holes therein, said support further comprising a conductiveplate having an aperture therein, said aperture being aligned with andbeing coextensive with less than all of said holes the remainder of saidholes being obscured by the solid portion of said plate, said platebeing secured to said shield means.

.3. An apparatus as described in claim 1 which further includes aplurality of conductive weights disposed within said holes adjacent saidcathode material, the height of said spacers being such that thethickness of said cathode material plus the height of said weight causesthe top of said weight to be less than the cathode dark space distancefrom said shield means.

4. An apparatus as described in claim 1 which further includes aconductive cylinder surrounding said conductive support means and beinginsulated therefrom, said cylinder being connected to said shield means.

5. An apparatus described claim 1 wherein said shield means comprisesfirst and second flat conductive portions having flanged edges at theperiphery thereof which overlap each other, said second shield portionhaving holes therein which are aligned with said apertures in saidcathode holder.

6. An apparatus as described in claim 5 which further includes aplurality of insulating spacers situated between said cathode holder andsaid first shield portion.

7. An apparatus as described in claim 1 which further includes means foradjusting the spacing between said shield means and said cathode holder.

8. An apparatus as described in claim 5 which further includes means toalign said holes in said second shield portion with said apertures insaid cathode holder.

".9. An apparatus as described in claim 8 wherein said means to aligncomprises a first plurality of alignment holes in said cathode holderand a second plurality of alignment holes in said first shield portionwhich are properly aligned with said first mentioned holes. and aplurality of insulating spacers disposed in and extending between saidfirst and second plurality of alignment holes.

110. An apparatus described in claim 9 wherein said means to alignfurther comprises a plurality of slots in the flanged portion of saidfirst shield portion and a plurality of setscrews located in the flangedportion of said 5 second shield portion, said setscrews being alignedwith 3,303,116 2/1967 Maissel et a1. 204192 said slots. 3,410,77411/1968 Barson et a1. 204192 References Cited I UNITED STATES PATENTSROBERT K. MIHALEK, Primary Examiner 3,282,815 11/1966 Kay et a1. 2041925 US. Cl. X.R.

3,296,115 1/1967 Laegreid et a1 204192 204192

